1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to a small-sized linear motion rolling contact guide unit using a rod rail suitable for use in precision measuring apparatuses and semiconductor facilities.
2. Description of the Prior Art
A linear motion rolling contact guide unit using a rod rail is well known in the art as disclosed, for example, in the Japanese Patent Lain-open Pub. No. 63-152719. The structure of the guide unit disclosed in this publication is illustrated here in FIGS. 4 through 7.
As shown in FIGS. 4 through 7, a linear motion rolling contact guide unit generally includes a rail 31 extending over a desired length, a slider 32 slidably mounted on the rail and a plurality of rolling members 33 interposed between the rail and the slider. The guide unit shown in FIGS. 4 through 7 has a characteristic feature in that its rail 31 is in the shape of a rod having a substantially circular cross section. In the illustrated example, the rod rail 31 is formed with a pair of upper and lower inner guide grooves 31a on each side thereof. As a result, the rod rail 31 is formed with four inner guide grooves 31a in total, each extending in parallel with the longitudinal axis of the rod rail 31.
The slider 32 generally includes a hollow cylindrical section through which the rod rail 31 extends and a flat mounting section, which is generally rectangular in shape and provided with a plurality (four in the illustrated example) of threaded mounting holes 32a one at each corner. Four endless circulating paths are provided in the hollow cylindrical section of the slider 32 and each of the endless circulating paths includes a load path section, a return path section and a pair of curved connecting path sections, each connecting the corresponding ends of the load and return path sections as well known in the art. An outer guide groove is formed in the inner peripheral surface of the hollow cylindrical section located opposite to its associated outer guide groove 31a as best shown in FIG. 6 so that the load section of each endless circulating path is defined by a pair of oppositely arranged inner and outer guide grooves. A plurality of rolling members or balls 33 in the illustrated example are provided in each of the endless circulating paths as best shown by the dotted lines in FIG. 5 so that the balls 33 roll along each of the endless circulating paths as the slider 32 moves along the rod rail 31, whereby those balls 33 which are located in the load path sections provide a rolling contact between the slider 32 and the rod rail 31.
Such a guide unit is typically mounted on a bed 34, for example, of a precision measuring apparatus or the like as shown in FIG. 7. Typically, two or more pairs of such guide units are provided and arranged in parallel to each other on the bed 34 or the like. The rod rail 31 is formed with a plurality of mounting holes 31b extending transversely across the rod rail 31, and the rod rail 31 is fixedly mounted on the bed 34 by means of bolts 35. For example, the bed 34 is provided with a block 36 having a raised end section formed with a V-shaped groove 36a for receiving therein an end portion of the rod rail 31. Since the slider 32 has a hollow cylindrical section which is loosely fitted onto the rod rail 31, the rod rail 31 must be located away or above the mounting block 36 so as to provide a continuous gap between the rod rail 31 and the mounting block 36. For this purpose, the mounting block 36 must have a raised section at each end.
As best shown in FIG. 7, since the flat mounting section of the slider 32 is formed with a plurality of threaded mounting holes 32a, the flat mounting section of the slider 32 may be fixedly attached to a sliding table 37 by means of bolts 38. The table 37 may be fixedly attached to two or more sliders 32 of other guide units which are arranged in parallel to each other. Any desired object, such as cutting tools or a work piece to be machined, may be mounted on the table 37 and the table 37 may be driven to move in any direction as indicated by a double arrow A.
Such a guide unit using a rod rail is particularly advantageous since it is simple in structure and thus easy and less expensive to manufacture. For example, the rod rail 31 is simple in structure and easy to fabricate. In addition, the rod rail 31 can be made smaller in size since its rigidity is relatively high. In additions, the slider 32 is also relatively simple in structure and thus easy to manufacture.
However, in the prior art guide unit using a rod rail as shown in FIGS. 4 through 7, since the slider 32 includes a hollow cylindrical section which completely surrounds the rod rail 31, difficulty may still be encountered in fabricating, in particular in molding and machining, the slider 32. In addition, because of such a completely surrounding structure, a continuous gap 36b between the rod rail 31 and the mounting block 36 must be provided along the entire stroke of the slider 32. As a result, there is a limit in locating the rod rail 31 closer to the mounting block 36, which, in turn, impairs the effort in making the overall size of the guide unit even smaller. Furthermore, since the rod rail 31 must be supported at its opposite ends only, the rod rail 31 may bend undesirably if the rod rail 31 is too long and/or too small in diameter. Thus, there is also a limit in making the overall size of the guide units smaller or larger.